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    <title>Document</title>
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<script>
    console.log(isNaN(NaN));//返回true
    console.log(isNaN("123"));//返回false(可以去转化数值123)
    console.log(isNaN(hello));//返回true(不可以去转化数值)
    console.log(isNaN(true));//返回false(可以去转化数值1)
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